Aperture stops in optical systems are used to define the largest bundle of rays from the scene that can pass through the system. In infrared imaging systems that view cold backgrounds, it is important that warm infrared radiation emitted from the aperture stop and other internal system elements do not contribute to the infrared signal that the detector “sees” from the intended scene. The unwanted signal from such an aperture stop and from warm internal structures inside the optical system is sometimes referred to as self emission or background infrared radiation. If this background infrared radiation is too high, an infrared imaging system may not be able to detect or discriminate faint targets against scenes with cold backgrounds.
Some conventional infrared imaging systems use cooled surfaces such as “cold shields” or “cold stops” to limit the contribution of background infrared radiation internal to the system. However the cooling mechanisms required to cool these surfaces are often costly, add unwanted weight and complexity, and cannot be easily incorporated due to space and packaging constraints. Thus there are general needs for methods and infrared imaging systems that reduce the detection of background infrared radiation from the system's internal sources.